The present invention relates generally to wheel suspension systems for vehicles and more particularly to a strut-type suspension for a vehicle which allows a wheel to independently adapt to terrain.
Wheel suspension systems have been developed in the prior art to control the attitude of wheel axles in order to provide handling characteristics, affect steering, and soften the ride characteristics. However, in the art of mobile work platforms, soft ride characteristics are not desirable since they create an unstable base which interferes with the platform lift functions. Nevertheless, mobile work platform vehicles are often driven across uneven terrain where it is desirable to maintain all wheels in contact with the ground at all times.
Independent suspension systems for mobile work platform vehicles have been absent in the prior art due most probably to the inherent problems in controlling the suspension sufficiently to provide safe lift operation. It is for this reason that prior independent suspension systems, such as that described in U.S. Pat. No. 4,458,913, which provides on each independent strut a spring cushion in conjunction with a shock absorber, cannot be used for a work platform vehicle. Although the spring and shock absorber will tend to maintain the controlled wheel in contact with the ground, the spring and shock absorber will tend to compress or yield in response to the motion of the platform when the platform is being elevated. Additionally, while this suspension system tends to maintain ground contact during motion of the vehicle, it generally does not provide sufficient contact force to ensure traction in rough terrain.
It is therefore an object of the present invention to provide a suspension system which locks into a stable position for lift operation. It is a further object of the invention to provide a suspension system which actively forces the wheels toward the ground to maintain sufficient contact force for wheel traction.